Overpass API developpement

[Malcolm Herring <>]

I need to perform an intersection, but there appears to be no native 
operator for this. So I am attempting to do this with unions & differences.

What I require: rel['key1'='value1'] AND rel['key2'='value2']

If I write: (rel['key1'='value1'] - rel['key2'!='value2'])

Will this work even if a relation in the input set has no tag with 
'key2'? I cannot find a definition of the "!=" operator.