ISO Pascal reference manual

*ERROR 17 -- is a reserved word and may not be used as
an identifier
Appendix A
The Pascal words which are known to the compiler: BEGIN, VAR, IF etc.
are reserved and must not be used to identify objects to be used in the
program
PROGRAM fail;
VAR from, to, high, low : integer; (TO is reserved)
BEGIN
END.
*ERROR 18 -- may not be used as a set operator
The only permissible set operators are + ' (set union), `-' (set difference),
"" (set intersection) and the comparison operators = < >', < =' and
t> =,.
PROGRAM fail;
VAR s,t,u:SET OF char;
BEGIN
END.
T :=
U :=
S := T / U; (what would this mean?)
*ERROR 20 -- has already been declared in this block
This error is generated when the compiler detects that < name > is being
declared for the second or subsequent time in a block. Each identifier in any
block may only have a unique meaning.
PROGRAM fail;
VAR max : integer; (correct declaration)
BEGIN
END.
n : char;
max : real; (max cannot be both integer and real)
Pascal Issue 1 51