diff --git a/src/lib/plainMath.ts b/src/lib/plainMath.ts
index 53c0b1c..4cbddce 100644
--- a/src/lib/plainMath.ts
+++ b/src/lib/plainMath.ts
@@ -67,7 +67,7 @@ export function plainMath(text: string): string {
   s = s.replace(/\^\(((?:[^()]|\([^()]*\))*)\)/g, (_m, a: string) => tryMap(a, SUP) ?? ` به توانِ (${a.trim()}) `);
   s = s.replace(/\^([+\-−]?[0-9۰-۹]+)/g, (m, a: string) => tryMap(a, SUP) ?? m);
   s = s.replace(/(?<=[A-Za-z0-9۰-۹)₀-₉])\^([A-Za-zα-ωΑ-Ω□])(?![A-Za-z0-9۰-۹])/g, (_m, a: string) => tryMap(a, SUP) ?? ` به توانِ ${a} `);
-  s = s.replace(/(?<=[A-Za-z)∫Σ∏])_([0-9۰-۹]+|[A-Za-z]{1,4}[0-9۰-۹]?)/g, (_m, a: string) => [...a].map((c) => SUB[c] ?? c).join(''));
+  s = s.replace(/((?<![A-Za-z0-9_])[A-Za-z]|log|ln|lim|[)∫Σ∏])_([0-9۰-۹]+[A-Za-z]?|[A-Za-z]{1,4}[0-9۰-۹]?)(?![A-Za-z0-9_])/g, (_m, p: string, a: string) => (p === 'log' && [...a].some((c) => !(c in SUB)) ? `log پایه‌ی ${a}` : p + [...a].map((c) => SUB[c] ?? c).join('')));
   s = s.replace(/\^([+\-−])/g, (_m, a: string) => SUP[a]);
   s = s.replace(/(?<=[A-Za-z)'])_([+\-−])/g, (_m, a: string) => SUB[a]);
   s = s.replace(/\^(√[0-9۰-۹A-Za-z]+)/g, ' به توانِ $1 ').replace(/\^([A-Za-z]{2,3})(?![A-Za-z0-9])/g, ' به توانِ $1 ');