SCREEN$ values do not allow internal maths

[gazj82]

The interpreter throws an error when trying to do internal maths in a SCREEN$ command.

3006 IF SCREEN$(x,y+3) =" " THEN GO TO 3006 throws the following error.

ERROR in line 3006, statement 1 - Expected ")", but got "+"

Thanks for the great program. I looked at the C code, but unfortunately it was beyond my capabilities.