diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
new file mode 100644
index 0000000..76d5715
--- /dev/null
+++ b/packages/core/src/index.ts
@@ -0,0 +1,4 @@
+/* eslint-disable no-console */
+const src = '$111$xxx$222$yyy\n$$\n\frac{1}{2}\n\frac{2}{3}\n$$'
+
+console.log(src.match(/\$\$[^]*\$\$/g).map(item => item.trim().replace(/\$*\n/, '').replace(/\n\$*$/, '').split(/\r?\n/).join('')))