My default shell is ksh. I'm making a simple comparison in a script.

...
if [${exists1} -eq 1] then
...

i keep getting the error " [1: not found". I've tried this comparison a number of different ways:
if [[${exists1} -eq 1]]
if [$exists1 -eq 1]
if [${exists1}== 1]
if [${exists1}= 1]
I have also tried all of these with parentheses instead of brackets, nothing works. I know exists1 (I expect it to be 1 in my tests) is being set properly, as is evidenced by the error. What's my problem?