This looks good.
Can we have a simpler test that runs faster?
Also, I note that we define knowledge bases with

   map(expr, ['A', 
                'B', 
                'C', ...])

could we just do

  expr("""A, 
          B, 
          C, ...""")

and since expr calls eval, wouldn't this just return a tuple of sub-exprs?

I was unable to get the second format to work in multiple lines. eval throws SyntaxError due to the new line characters. I tried to use ''' inside """ but that didn't work either. I think it is better to leave it as it is. Using techniques to ignore the newline character would only make it harder to read.