Many spelling fixes in comments.  No changes to code.

FossilOrigin-Name: 6f6e2d50941e444ebc83604daddcc034137a05b7
diff --git a/src/expr.c b/src/expr.c
index ed5451b..ae6a1de 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -3542,7 +3542,7 @@
   int r1, r2;
 
   assert( jumpIfNull==SQLITE_JUMPIFNULL || jumpIfNull==0 );
-  if( NEVER(v==0) )     return;  /* Existance of VDBE checked by caller */
+  if( NEVER(v==0) )     return;  /* Existence of VDBE checked by caller */
   if( NEVER(pExpr==0) ) return;  /* No way this can happen */
   op = pExpr->op;
   switch( op ){
@@ -3662,7 +3662,7 @@
   int r1, r2;
 
   assert( jumpIfNull==SQLITE_JUMPIFNULL || jumpIfNull==0 );
-  if( NEVER(v==0) ) return; /* Existance of VDBE checked by caller */
+  if( NEVER(v==0) ) return; /* Existence of VDBE checked by caller */
   if( pExpr==0 )    return;
 
   /* The value of pExpr->op and op are related as follows: