--- a/progs/lexer/lexer.sc	Wed Feb 21 09:14:12 2024 +0000
+++ b/progs/lexer/lexer.sc	Wed May 29 13:25:30 2024 +0100
@@ -59,7 +59,7 @@
   case ONE => true
   case CHAR(_) => false
   case ALT(r1, r2) => nullable(r1) || nullable(r2)
-  case SEQ(r1, r2) => nullable(r1) $$ nullable(r2)
+  case SEQ(r1, r2) => nullable(r1) && nullable(r2)
   case STAR(_) => true
   case RECD(_, r1) => nullable(r1)
 }