diff --git a/rsconcept/frontend/src/components/info/InfoConstituenta.tsx b/rsconcept/frontend/src/components/info/InfoConstituenta.tsx
index cbcd3183..51615be9 100644
--- a/rsconcept/frontend/src/components/info/InfoConstituenta.tsx
+++ b/rsconcept/frontend/src/components/info/InfoConstituenta.tsx
@@ -1,3 +1,5 @@
+import clsx from 'clsx';
+
 import { IConstituenta } from '@/models/rsform';
 import { labelCstTypification } from '@/utils/labels';
 
@@ -7,9 +9,9 @@ interface InfoConstituentaProps extends CProps.Div {
   data: IConstituenta;
 }
 
-function InfoConstituenta({ data, ...restProps }: InfoConstituentaProps) {
+function InfoConstituenta({ data, className, ...restProps }: InfoConstituentaProps) {
   return (
-    <div {...restProps}>
+    <div className={clsx('dense', className)} {...restProps}>
       <h2>Конституента {data.alias}</h2>
       <p>
         <b>Типизация: </b>
diff --git a/rsconcept/frontend/src/components/info/InfoCstClass.tsx b/rsconcept/frontend/src/components/info/InfoCstClass.tsx
index 94fce698..f1f5a686 100644
--- a/rsconcept/frontend/src/components/info/InfoCstClass.tsx
+++ b/rsconcept/frontend/src/components/info/InfoCstClass.tsx
@@ -14,7 +14,7 @@ function InfoCstClass({ header }: InfoCstClassProps) {
   const { colors } = useConceptTheme();
 
   return (
-    <div className='flex flex-col gap-1 mb-2'>
+    <div className='flex flex-col gap-1 mb-2 dense'>
       {header ? <h1>{header}</h1> : null}
       {Object.values(CstClass).map((cstClass, index) => {
         return (
diff --git a/rsconcept/frontend/src/components/info/InfoCstStatus.tsx b/rsconcept/frontend/src/components/info/InfoCstStatus.tsx
index 9fd9872a..dda547c6 100644
--- a/rsconcept/frontend/src/components/info/InfoCstStatus.tsx
+++ b/rsconcept/frontend/src/components/info/InfoCstStatus.tsx
@@ -14,7 +14,7 @@ function InfoCstStatus({ title }: InfoCstStatusProps) {
   const { colors } = useConceptTheme();
 
   return (
-    <div className='flex flex-col gap-1 mb-2'>
+    <div className='flex flex-col gap-1 mb-2 dense'>
       {title ? <h1>{title}</h1> : null}
       {Object.values(ExpressionStatus)
         .filter(status => status !== ExpressionStatus.UNDEFINED)
diff --git a/rsconcept/frontend/src/components/wrap/AnimateFade.tsx b/rsconcept/frontend/src/components/wrap/AnimateFade.tsx
index 2861a456..f30b4dd9 100644
--- a/rsconcept/frontend/src/components/wrap/AnimateFade.tsx
+++ b/rsconcept/frontend/src/components/wrap/AnimateFade.tsx
@@ -7,14 +7,29 @@ import { CProps } from '../props';
 interface AnimateFadeProps extends CProps.AnimatedDiv {
   noFadeIn?: boolean;
   noFadeOut?: boolean;
+  removeContent?: boolean;
+  hideContent?: boolean;
 }
 
-function AnimateFade({ noFadeIn, noFadeOut, children, ...restProps }: AnimateFadeProps) {
+function AnimateFade({
+  style,
+  noFadeIn,
+  noFadeOut,
+  children,
+  removeContent,
+  hideContent,
+  ...restProps
+}: AnimateFadeProps) {
+  if (removeContent) {
+    return null;
+  }
   return (
     <motion.div
       initial={{ ...(!noFadeIn ? animateFade.initial : {}) }}
-      animate={{ ...animateFade.animate }}
+      animate={hideContent ? 'hidden' : 'active'}
+      variants={animateFade.variants}
       exit={{ ...(!noFadeOut ? animateFade.exit : {}) }}
+      style={{ display: hideContent ? 'none' : '', ...style }}
       {...restProps}
     >
       {children}
diff --git a/rsconcept/frontend/src/components/wrap/DataLoader.tsx b/rsconcept/frontend/src/components/wrap/DataLoader.tsx
index 0b01adbc..f48ceca6 100644
--- a/rsconcept/frontend/src/components/wrap/DataLoader.tsx
+++ b/rsconcept/frontend/src/components/wrap/DataLoader.tsx
@@ -1,9 +1,9 @@
 import { AnimatePresence } from 'framer-motion';
 
-import AnimateFade from './AnimateFade';
 import InfoError, { ErrorData } from '../info/InfoError';
 import { CProps } from '../props';
 import Loader from '../ui/Loader';
+import AnimateFade from './AnimateFade';
 
 interface DataLoaderProps extends CProps.AnimatedDiv {
   id: string;
@@ -20,16 +20,12 @@ function DataLoader({ id, isLoading, hasNoData, error, children, ...restProps }:
     <AnimatePresence mode='wait'>
       {isLoading ? <Loader key={`${id}-loader`} /> : null}
       {error ? <InfoError key={`${id}-error`} error={error} /> : null}
-      {!isLoading && !error && !hasNoData ? (
-        <AnimateFade id={id} key={`${id}-data`} {...restProps}>
-          {children}
-        </AnimateFade>
-      ) : null}
-      {!isLoading && !error && hasNoData ? (
-        <AnimateFade id={id} key={`${id}-data`} {...restProps}>
-          Данные не загружены
-        </AnimateFade>
-      ) : null}
+      <AnimateFade id={id} key={`${id}-data`} removeContent={isLoading || !!error || hasNoData} {...restProps}>
+        {children}
+      </AnimateFade>
+      <AnimateFade id={id} key={`${id}-data`} removeContent={isLoading || !!error || !hasNoData} {...restProps}>
+        Данные не загружены
+      </AnimateFade>
     </AnimatePresence>
   );
 }
diff --git a/rsconcept/frontend/src/models/rsformAPI.ts b/rsconcept/frontend/src/models/rsformAPI.ts
index ad3e4c8d..5bd14f20 100644
--- a/rsconcept/frontend/src/models/rsformAPI.ts
+++ b/rsconcept/frontend/src/models/rsformAPI.ts
@@ -239,7 +239,7 @@ export function applyFilterCategory(start: IConstituenta, schema: IRSFormData):
 /**
  * Prefix for alias indicating {@link CstType}.
  */
-export function getCstTypePrefix(type: CstType) {
+export function getCstTypePrefix(type: CstType): string {
   // prettier-ignore
   switch (type) {
     case CstType.BASE: return 'X';
@@ -256,7 +256,7 @@ export function getCstTypePrefix(type: CstType) {
 /**
  * Guess {@link CstType} from user input hint.
  */
-export function guessCstType(hint: string, defaultType: CstType = CstType.TERM) {
+export function guessCstType(hint: string, defaultType: CstType = CstType.TERM): CstType {
   if (hint.length !== 1) {
     return defaultType;
   }
@@ -274,6 +274,57 @@ export function guessCstType(hint: string, defaultType: CstType = CstType.TERM)
   return defaultType;
 }
 
+/**
+ * Evaluate if {@link CstType} is basic concept.
+ */
+export function isBasicConcept(type: CstType): boolean {
+  // prettier-ignore
+  switch (type) {
+    case CstType.BASE: return true;
+    case CstType.CONSTANT: return true;
+    case CstType.STRUCTURED: return true;
+    case CstType.AXIOM: return true;
+    case CstType.TERM: return false;
+    case CstType.FUNCTION: return false;
+    case CstType.PREDICATE: return false;
+    case CstType.THEOREM: return false;
+  }
+}
+
+/**
+ * Evaluate if {@link CstType} is base set or constant set.
+ */
+export function isBaseSet(type: CstType): boolean {
+  // prettier-ignore
+  switch (type) {
+    case CstType.BASE: return true;
+    case CstType.CONSTANT: return true;
+    case CstType.STRUCTURED: return false;
+    case CstType.AXIOM: return false;
+    case CstType.TERM: return false;
+    case CstType.FUNCTION: return false;
+    case CstType.PREDICATE: return false;
+    case CstType.THEOREM: return false;
+  }
+}
+
+/**
+ * Evaluate if {@link CstType} is function.
+ */
+export function isFunctional(type: CstType): boolean {
+  // prettier-ignore
+  switch (type) {
+    case CstType.BASE: return false;
+    case CstType.CONSTANT: return false;
+    case CstType.STRUCTURED: return false;
+    case CstType.AXIOM: return false;
+    case CstType.TERM: return false;
+    case CstType.FUNCTION: return true;
+    case CstType.PREDICATE: return true;
+    case CstType.THEOREM: return false;
+  }
+}
+
 /**
  * Validate new alias against {@link CstType} and {@link IRSForm}.
  */
diff --git a/rsconcept/frontend/src/pages/RSFormPage/EditorConstituenta/FormConstituenta.tsx b/rsconcept/frontend/src/pages/RSFormPage/EditorConstituenta/FormConstituenta.tsx
index d6ec1fff..4ee6fcfc 100644
--- a/rsconcept/frontend/src/pages/RSFormPage/EditorConstituenta/FormConstituenta.tsx
+++ b/rsconcept/frontend/src/pages/RSFormPage/EditorConstituenta/FormConstituenta.tsx
@@ -1,15 +1,18 @@
 'use client';
 
 import clsx from 'clsx';
-import { useEffect, useLayoutEffect, useState } from 'react';
+import { AnimatePresence } from 'framer-motion';
+import { useEffect, useLayoutEffect, useMemo, useState } from 'react';
 import { FiSave } from 'react-icons/fi';
 import { toast } from 'react-toastify';
 
 import RefsInput from '@/components/RefsInput';
 import SubmitButton from '@/components/ui/SubmitButton';
 import TextArea from '@/components/ui/TextArea';
+import AnimateFade from '@/components/wrap/AnimateFade';
 import { useRSForm } from '@/context/RSFormContext';
-import { IConstituenta, ICstUpdateData } from '@/models/rsform';
+import { CstType, IConstituenta, ICstUpdateData } from '@/models/rsform';
+import { isBaseSet, isBasicConcept, isFunctional } from '@/models/rsformAPI';
 import { labelCstTypification } from '@/utils/labels';
 
 import EditorRSExpression from '../EditorRSExpression';
@@ -40,9 +43,11 @@ function FormConstituenta({
   disabled,
   showList,
   id,
+  constituenta,
+
   isModified,
   setIsModified,
-  constituenta,
+
   toggleReset,
   onRename,
   onEditTerm,
@@ -56,6 +61,14 @@ function FormConstituenta({
   const [expression, setExpression] = useState('');
   const [convention, setConvention] = useState('');
   const [typification, setTypification] = useState('N/A');
+  const [forceComment, setForceComment] = useState(false);
+
+  const isBasic = useMemo(() => !!constituenta && isBasicConcept(constituenta.cst_type), [constituenta]);
+  const isElementary = useMemo(() => !!constituenta && isBaseSet(constituenta.cst_type), [constituenta]);
+  const showConvention = useMemo(
+    () => !constituenta || !!constituenta.convention || forceComment || isBasic,
+    [constituenta, forceComment, isBasic]
+  );
 
   useEffect(() => {
     if (!constituenta) {
@@ -90,6 +103,7 @@ function FormConstituenta({
       setTextDefinition(constituenta.definition_raw || '');
       setExpression(constituenta.definition_formal || '');
       setTypification(constituenta ? labelCstTypification(constituenta) : 'N/A');
+      setForceComment(false);
     }
   }, [constituenta, schema, toggleReset]);
 
@@ -126,73 +140,101 @@ function FormConstituenta({
         className={clsx('cc-column', 'mt-1 w-full md:w-[47.8rem] shrink-0', 'px-4 py-1')}
         onSubmit={handleSubmit}
       >
-        <RefsInput
-          id='cst_term'
-          label='Термин'
-          placeholder='Обозначение, используемое в текстовых определениях'
-          items={schema?.items}
-          value={term}
-          initialValue={constituenta?.term_raw ?? ''}
-          resolved={constituenta?.term_resolved ?? ''}
-          disabled={disabled}
-          onChange={newValue => setTerm(newValue)}
-        />
-        <TextArea
-          id='cst_typification'
-          dense
-          noBorder
-          disabled={true}
-          label='Типизация'
-          rows={typification.length > ROW_SIZE_IN_CHARACTERS ? 2 : 1}
-          value={typification}
-          colors='clr-app'
-          style={{
-            resize: 'none'
-          }}
-        />
-        <EditorRSExpression
-          id='cst_expression'
-          label='Формальное определение'
-          placeholder='Родоструктурное выражение'
-          value={expression}
-          activeCst={constituenta}
-          showList={showList}
-          disabled={disabled}
-          toggleReset={toggleReset}
-          onToggleList={onToggleList}
-          onChange={newValue => setExpression(newValue)}
-          setTypification={setTypification}
-        />
-        <RefsInput
-          id='cst_definition'
-          label='Текстовое определение'
-          placeholder='Текстовая интерпретация формального выражения'
-          height='3.8rem'
-          items={schema?.items}
-          value={textDefinition}
-          initialValue={constituenta?.definition_raw ?? ''}
-          resolved={constituenta?.definition_resolved ?? ''}
-          disabled={disabled}
-          onChange={newValue => setTextDefinition(newValue)}
-        />
-        <TextArea
-          id='cst_convention'
-          spellCheck
-          label='Конвенция / Комментарий'
-          placeholder='Договоренность об интерпретации или пояснение'
-          value={convention}
-          disabled={disabled}
-          rows={convention.length > 2 * ROW_SIZE_IN_CHARACTERS ? 3 : 2}
-          onChange={event => setConvention(event.target.value)}
-        />
-        {!disabled || processing ? (
-          <SubmitButton
-            text='Сохранить изменения'
-            className='self-center'
-            disabled={disabled || !isModified}
-            icon={<FiSave size='1.25rem' />}
+        <AnimatePresence>
+          <RefsInput
+            id='cst_term'
+            label='Термин'
+            placeholder='Обозначение, используемое в текстовых определениях'
+            items={schema?.items}
+            value={term}
+            initialValue={constituenta?.term_raw ?? ''}
+            resolved={constituenta?.term_resolved ?? ''}
+            disabled={disabled}
+            onChange={newValue => setTerm(newValue)}
           />
-        ) : null}
+          <TextArea
+            id='cst_typification'
+            dense
+            noBorder
+            disabled={true}
+            label='Типизация'
+            rows={typification.length > ROW_SIZE_IN_CHARACTERS ? 2 : 1}
+            value={typification}
+            colors='clr-app'
+            style={{
+              resize: 'none'
+            }}
+          />
+          <AnimateFade hideContent={!!constituenta && !constituenta?.definition_formal && isElementary}>
+            <EditorRSExpression
+              id='cst_expression'
+              label={
+                constituenta?.cst_type === CstType.STRUCTURED
+                  ? 'Область определения'
+                  : !!constituenta && isFunctional(constituenta.cst_type)
+                  ? 'Определение функции'
+                  : 'Формальное определение'
+              }
+              placeholder={
+                constituenta?.cst_type !== CstType.STRUCTURED
+                  ? 'Родоструктурное выражение'
+                  : 'Определение множества, которому принадлежат элементы родовой структуры'
+              }
+              value={expression}
+              activeCst={constituenta}
+              showList={showList}
+              disabled={disabled}
+              toggleReset={toggleReset}
+              onToggleList={onToggleList}
+              onChange={newValue => setExpression(newValue)}
+              setTypification={setTypification}
+            />
+          </AnimateFade>
+          <AnimateFade hideContent={!!constituenta && !constituenta?.definition_raw && isElementary}>
+            <RefsInput
+              id='cst_definition'
+              label='Текстовое определение'
+              placeholder='Текстовая интерпретация формального выражения'
+              height='3.8rem'
+              items={schema?.items}
+              value={textDefinition}
+              initialValue={constituenta?.definition_raw ?? ''}
+              resolved={constituenta?.definition_resolved ?? ''}
+              disabled={disabled}
+              onChange={newValue => setTextDefinition(newValue)}
+            />
+          </AnimateFade>
+          <AnimateFade hideContent={!showConvention}>
+            <TextArea
+              id='cst_convention'
+              spellCheck
+              className='h-[3.8rem]'
+              label={isBasic ? 'Конвенция' : 'Комментарий'}
+              placeholder='Договоренность об интерпретации или пояснение'
+              value={convention}
+              disabled={disabled}
+              rows={convention.length > 2 * ROW_SIZE_IN_CHARACTERS ? 3 : 2}
+              onChange={event => setConvention(event.target.value)}
+            />
+          </AnimateFade>
+          {!showConvention && (!disabled || processing) ? (
+            <button
+              type='button'
+              className='self-start cc-label clr-text-url hover:underline'
+              onClick={() => setForceComment(true)}
+            >
+              Добавить комментарий
+            </button>
+          ) : null}
+          {!disabled || processing ? (
+            <SubmitButton
+              text='Сохранить изменения'
+              className='self-center'
+              disabled={disabled || !isModified}
+              icon={<FiSave size='1.25rem' />}
+            />
+          ) : null}
+        </AnimatePresence>
       </form>
     </div>
   );
diff --git a/rsconcept/frontend/src/pages/RSFormPage/EditorRSExpression/RSEditControls.tsx b/rsconcept/frontend/src/pages/RSFormPage/EditorRSExpression/RSEditControls.tsx
index 6e6ba949..bded37bc 100644
--- a/rsconcept/frontend/src/pages/RSFormPage/EditorRSExpression/RSEditControls.tsx
+++ b/rsconcept/frontend/src/pages/RSFormPage/EditorRSExpression/RSEditControls.tsx
@@ -49,7 +49,7 @@ const MAIN_THIRD_ROW: TokenID[] = [
   TokenID.LOGIC_EQUIVALENT,
   TokenID.SET_SYMMETRIC_MINUS,
   TokenID.PUNCTUATION_ASSIGN,
-  TokenID.EQUAL,
+  TokenID.MULTIPLY,
   TokenID.GREATER_OR_EQ,
   TokenID.LESSER_OR_EQ
 ];
diff --git a/rsconcept/frontend/src/pages/RegisterPage.tsx b/rsconcept/frontend/src/pages/RegisterPage.tsx
index 26d960f8..d15607e9 100644
--- a/rsconcept/frontend/src/pages/RegisterPage.tsx
+++ b/rsconcept/frontend/src/pages/RegisterPage.tsx
@@ -65,7 +65,11 @@ function RegisterPage() {
   }
 
   if (user) {
-    return <ExpectedAnonymous />;
+    return (
+      <AnimateFade>
+        <ExpectedAnonymous />
+      </AnimateFade>
+    );
   }
   return (
     <AnimateFade>
diff --git a/rsconcept/frontend/src/styling/animations.ts b/rsconcept/frontend/src/styling/animations.ts
index 83a8f867..dc85a695 100644
--- a/rsconcept/frontend/src/styling/animations.ts
+++ b/rsconcept/frontend/src/styling/animations.ts
@@ -216,12 +216,22 @@ export const animateFade = {
   initial: {
     opacity: 0
   },
-  animate: {
-    opacity: 1,
-    transition: {
-      type: 'tween',
-      ease: 'linear',
-      duration: 0.3
+  variants: {
+    active: {
+      opacity: 1,
+      transition: {
+        type: 'tween',
+        ease: 'linear',
+        duration: 0.3
+      }
+    },
+    hidden: {
+      opacity: 0,
+      transition: {
+        type: 'tween',
+        ease: 'linear',
+        duration: 0.3
+      }
     }
   },
   exit: {
diff --git a/rsconcept/frontend/src/utils/codemirror.ts b/rsconcept/frontend/src/utils/codemirror.ts
index a5ca510b..643cee2e 100644
--- a/rsconcept/frontend/src/utils/codemirror.ts
+++ b/rsconcept/frontend/src/utils/codemirror.ts
@@ -129,10 +129,11 @@ export function domTooltipConstituenta(cst?: IConstituenta) {
   dom.className = clsx(
     'z-modal-tooltip',
     'max-h-[25rem] max-w-[25rem] min-w-[10rem]',
+    'dense',
     'p-2',
     'border shadow-md',
     'overflow-y-auto',
-    'text-sm'
+    'text-sm font-main'
   );
 
   if (cst) {
@@ -179,6 +180,7 @@ export function domTooltipEntityReference(ref: IEntityReference, cst: IConstitue
   dom.className = clsx(
     'z-tooltip',
     'max-h-[25rem] max-w-[25rem] min-w-[10rem]',
+    'dense',
     'p-2 flex flex-col',
     'border shadow-md',
     'overflow-y-auto',
@@ -225,6 +227,7 @@ export function domTooltipSyntacticReference(ref: ISyntacticReference, masterRef
   dom.className = clsx(
     'z-tooltip',
     'max-h-[25rem] max-w-[25rem] min-w-[10rem]',
+    'dense',
     'p-2 flex flex-col',
     'border shadow-md',
     'overflow-y-auto',
diff --git a/rsconcept/frontend/src/utils/labels.ts b/rsconcept/frontend/src/utils/labels.ts
index e8d3214e..e53038fa 100644
--- a/rsconcept/frontend/src/utils/labels.ts
+++ b/rsconcept/frontend/src/utils/labels.ts
@@ -96,6 +96,7 @@ export function labelToken(id: TokenID): string {
     case TokenID.LOGIC_EQUIVALENT:    return '⇔';
     case TokenID.LIT_EMPTYSET:        return '∅';
     case TokenID.LIT_WHOLE_NUMBERS:   return 'Z';
+    case TokenID.MULTIPLY:            return '*';
     case TokenID.EQUAL:               return '=';
     case TokenID.NOTEQUAL:            return '≠';
     case TokenID.GREATER_OR_EQ:       return '≥';
@@ -163,6 +164,7 @@ export function describeToken(id: TokenID): string {
     case TokenID.LIT_EMPTYSET:          return prepareTooltip('Пустое множество', 'Alt + X');
     case TokenID.LIT_WHOLE_NUMBERS:     return prepareTooltip('Целые числа', 'Alt + Z');
     case TokenID.EQUAL:                 return prepareTooltip('Равенство');
+    case TokenID.MULTIPLY:              return prepareTooltip('Умножение чисел', 'Alt + 8');
     case TokenID.NOTEQUAL:              return prepareTooltip('Неравенство', 'Alt + Shift + `');
     case TokenID.GREATER_OR_EQ:         return prepareTooltip('Больше или равно', 'Alt + Shift + 7');
     case TokenID.LESSER_OR_EQ:          return prepareTooltip('Меньше или равно', 'Alt + Shift + 8');