HI! Can someone help me with this LISP programming question?

From what I understand, we are given the type (sigmoid or asigmoid) and a sum, but I don't know what the sum is used for?? I think I'm a little confused as to what the question is asking for (I'm fairly new to LISP)...

Use cond and exp to define (activation type sum) which returns the activation value of a connectionist unit given a sum of products of input activations x corresponding connection weights. Include both 'sigmoid and 'asigmoid types of activation functions, and return unknown-type if some other type is used as input. Sigmoid type: y 0.5 1+e Asigmoid type: y,-- where xj is the sum of net input to unit j. , Use cond and exp to define (activation type sum) which returns the activation value of a connectionist unit given a sum of products of input activations x corresponding connection weights. Include both 'sigmoid and 'asigmoid types of activation functions, and return unknown-type if some other type is used as input. Sigmoid type: y 0.5 1+e Asigmoid type: y,-- where xj is the sum of net input to unit j