diff --git a/kmath-ast/reference/ArithmeticsEvaluator.g4 b/kmath-ast/reference/ArithmeticsEvaluator.g4
index 684a9de44..137d42860 100644
--- a/kmath-ast/reference/ArithmeticsEvaluator.g4
+++ b/kmath-ast/reference/ArithmeticsEvaluator.g4
@@ -2,9 +2,10 @@ grammar ArithmeticsEvaluator;
 
 fragment DIGIT: '0'..'9';
 fragment LETTER: 'a'..'z';
+fragment CAPITAL_LETTER: 'A'..'Z'
 fragment UNDERSCORE: '_';
 
-ID: (LETTER | UNDERSCORE) (LETTER | UNDERSCORE | DIGIT)*;
+ID: (LETTER | UNDERSCORE | CAPITAL_LETTER) (LETTER | UNDERSCORE | DIGIT | CAPITAL_LETTER)*;
 NUM: (DIGIT | '.')+ ([eE] MINUS? DIGIT+)?;
 MUL: '*';
 DIV: '/';
diff --git a/kmath-ast/src/commonMain/kotlin/scientifik/kmath/ast/parser.kt b/kmath-ast/src/commonMain/kotlin/scientifik/kmath/ast/parser.kt
index ae0b6656d..27f133d6a 100644
--- a/kmath-ast/src/commonMain/kotlin/scientifik/kmath/ast/parser.kt
+++ b/kmath-ast/src/commonMain/kotlin/scientifik/kmath/ast/parser.kt
@@ -19,7 +19,7 @@ import scientifik.kmath.operations.SpaceOperations
  */
 object ArithmeticsEvaluator : Grammar<MST>() {
     private val num: Token by token("[\\d.]+(?:[eE]-?\\d+)?".toRegex())
-    private val id: Token by token("[a-z_][\\da-z_]*".toRegex())
+    private val id: Token by token("[a-z_A-Z][\\da-z_A-Z]*".toRegex())
     private val lpar: Token by token("\\(".toRegex())
     private val rpar: Token by token("\\)".toRegex())
     private val comma: Token by token(",".toRegex())