I'm messing about with Project Euler problems and have noticed some behavior that I don't understand. This one happens to be very self-contained so I though I'd as for assistance. This code (which doesn't solve the problem, btw) is buggy, but I can't see the bug and I'm beginning to suspect something in the VM or the class libraries. When I execute it, two odd things happen: First, in spite of the block test [sum < 100] whileTrue:[...] it continues to run when sum > 100 (or a million for that matter). Second, the block in the line: (sum isPrime) ifTrue: [ (seq size > bestSeq size) ifTrue: [ bestSeq := seq copy.]] executes even when sum is not a prime number. Any help is appreciated. ------------------------------- "Create a list of primes smaller than a million" primes := OrderedCollection new. 2 to: 999999 do: [ :n | n isPrime ifTrue: [ primes add: n]]. bestSeq := OrderedCollection new. seq := OrderedCollection new. sum := 0. [sum < 100] whileTrue: [ primes do: [:prime | seq add: prime. sum := seq sum. (sum isPrime) ifTrue: [ (seq size > bestSeq size) ifTrue: [ bestSeq := seq copy.]] ] ].