how should 'a + b > c + d' work ?

[k2s]

'a + b > c + d' - binds to the 'a', 'b', 'c' and 'd' keys. Pressing both the 'a' key and the 'b' key, then both the 'c' and the 'd' key will match this keyCombo.

does it mean I have to press and keep pressed all keys to fire the event ?
is there a way to press a+b ... all keys up ... press c+d to fire the event ?

[RobertWHurst]

It means the a and b keys must be pressed and held, then the c and d keys must also be pressed. They can be released in any order. As for pressing one key releasing it and then pressing another, this is something that you should be able to do yourself. You just need to keep track of which keys have been pressed with an array. As soon as an incorrect key is pressed then empty your array.