You can use &&
to check for both conditions. The overall evaluation is true only if both the operands are true. This operator exists for many (C-like) languages
Like:
lard :: (Integral a) => a
lard = head ( filter p[100,99..])
where p x = (x `mod` 13 == 0) && (x `mod` 7 == 0)
Warning: There might be better ways of doing this. I just stepped into the world of Haskell. :)