I am looking for a math editor that is able to present equations and relations between them. I am not searching for a traditional Latex / MathML editor (I know about various online services that allow typing in equations in various formats then outputting a pretty picture). I know about online sage notebook, about mathjax and that like. I also know about Lurch and Wolfram Alpha (thanks to tp1 below).
What I'm looking for is something like pearltrees in interface with pearls being equations and edges indicating the source of the concepts (other equations or axioms). The equations should be editable and each may have an additional page that explains the equation, maybe from external source like Wikipedia.
Consider two even integers x and y. Since they are even, they can be written as x = 2a and y = 2b respectively for integers a and b. Then the sum x + y = 2a + 2b = 2(a + b). From this it is clear x + y has 2 as a factor and therefore is even, so the sum of any two even integers is even.
(can't embed images yet)