diff --git a/src/Expressions/FunctionCallExpression.fu b/src/Expressions/FunctionCallExpression.fu
index 060b1bf..aa8e664 100644
--- a/src/Expressions/FunctionCallExpression.fu
+++ b/src/Expressions/FunctionCallExpression.fu
@@ -16,9 +16,12 @@ class FunctionCallExpressionSin : FunctionCallExpression {
 class FunctionCallExpressionCos : FunctionCallExpression {
     internal override double FunctionImplementation(double x) => Math.Cos(x);
 }
-class FunctionCallExpressionTan : FunctionCallExpression {
+class FunctionCallExpressionTg : FunctionCallExpression {
     internal override double FunctionImplementation(double x) => Math.Tan(x);
 }
+class FunctionCallExpressionCtg : FunctionCallExpression {
+    internal override double FunctionImplementation(double x) => 1 / Math.Tan(x);
+}
 
 class FunctionCallExpressionAsin : FunctionCallExpression {
     internal override double FunctionImplementation(double x) => Math.Asin(x);
@@ -26,10 +29,13 @@ class FunctionCallExpressionAsin : FunctionCallExpression {
 class FunctionCallExpressionAcos : FunctionCallExpression {
     internal override double FunctionImplementation(double x) => Math.Acos(x);
 }
-class FunctionCallExpressionAtan : FunctionCallExpression {
+class FunctionCallExpressionAtg : FunctionCallExpression {
     internal override double FunctionImplementation(double x) => Math.Atan(x);
 }
+class FunctionCallExpressionActg : FunctionCallExpression {
+    internal override double FunctionImplementation(double x) => Math.Atan(1 / x);
+}
 
-class FunctionCallExpressionLog : FunctionCallExpression{
+class FunctionCallExpressionLn : FunctionCallExpression{
     internal override double FunctionImplementation(double x) => Math.Log(x);
 }
diff --git a/src/Parser.fu b/src/Parser.fu
index b4f4dc4..8309002 100644
--- a/src/Parser.fu
+++ b/src/Parser.fu
@@ -119,7 +119,11 @@ class Parser {
                             PushFunctionExpression(expressionStack, str, new FunctionCallExpressionCos());
                             break;
                         case "tan":
-                            PushFunctionExpression(expressionStack, str, new FunctionCallExpressionTan());
+                        case "tg":
+                            PushFunctionExpression(expressionStack, str, new FunctionCallExpressionTg());
+                            break;
+                        case "ctg":
+                            PushFunctionExpression(expressionStack, str, new FunctionCallExpressionCtg());
                             break;
                         case "asin":
                             PushFunctionExpression(expressionStack, str, new FunctionCallExpressionAsin());
@@ -128,10 +132,16 @@ class Parser {
                             PushFunctionExpression(expressionStack, str, new FunctionCallExpressionAcos());
                             break;
                         case "atan":
-                            PushFunctionExpression(expressionStack, str, new FunctionCallExpressionAtan());
+                        case "atg":
+                        case "arctg":
+                            PushFunctionExpression(expressionStack, str, new FunctionCallExpressionAtg());
                             break;
-                        case "log":
-                            PushFunctionExpression(expressionStack, str, new FunctionCallExpressionLog());
+                        case "actg":
+                        case "arcctg":
+                            PushFunctionExpression(expressionStack, str, new FunctionCallExpressionActg());
+                            break;
+                        case "ln":
+                            PushFunctionExpression(expressionStack, str, new FunctionCallExpressionLn());
                             break;
                         default: {
                             ThrowError($"invalid literal '{str}'");