. package:QuickCheck

Conjunction: p1 .&&. p2 passes if both p1 and p2 pass.
Nondeterministic choice: p1 .&. p2 picks randomly one of p1 and p2 to test. If you test the property 100 times it makes 100 random choices.
Disjunction: p1 .||. p2 passes unless p1 and p2 simultaneously fail.