transitivity

My intention was to implement a simple example (just for myself) of transitivity in Prolog. These are my facts: trust_direct(p1, p2). trust_direct(p1, p3). trust_direct(p2, p4). trust_direct(p2, p5). trust_direct(p5, p6). trust_direct(p6, p7). trust_direct(p7, p8). trust_direct(p100, p200). I've written this predicate to check whether A trusts C , which is true whenever there is a B that trusts C and A trusts this B : trusts(A, B) :- trust_direct(A, B). trusts(A, C) :- trusts(A, B), trusts(B, C). The predicate returns true for trusts(p1, p2) or trusts(p1, p5) for example, but trusts(p5, p6)

I've been reading Douglas Crockford's JavaScript: The Good Parts , and I came across this weird example that doesn't make sense to me: '' == '0' // false 0 == '' // true 0 == '0' // true false == undefined // false false == null // false null == undefined // true The author also goes on to mention "to never use == and != . Instead, always use === and !== ". However, he doesn't explain why the above behavior is exhibited? So my question is, why are the above results as they are? Isn't transitivity considered in JavaScript? alex '' == '0' // false The left hand side is an empty string, and the