Proc Format: character variables & range

[apple]

proc format;

value $YrPur

low -<1989'='before 1989'

'1989'-'1998'='1989-1998'

'1999'-'2003' ='1999-2003'

'2004'-'2008' ='2004-2008'

'2009'-'2013'='2009-2013';

run;

The variable the format to be applied on is character but with numeric values.

Where should I add the quote marks for this range: low -<1989?

Thanks

[PGStats]

low -<'1989'

LOW is a keyword, it doesn't require quotes.

PG