v2 rollback SEQ operator (declaring z inside body yielded wrong resul…

…t in test) + add EIS

src/operators.jl

@@ -5,10 +5,7 @@ Sequence operator (Pólya quasi-inverse operator).
 
 Defined as ``A = SEQ(B) \\implies A(z) = \\frac{1}{1 - B(z)}``.
 """
-function SEQ(z)
-    z = SymPy.symbols("z")
-    return(1/(1-z))
-end
+SEQ(z) = 1/(1-z)
 
 
 """
@@ -19,7 +16,6 @@ Multiset operator (Pólya exponential operator).
 Defined as ``A = MSET(B) \\implies A(z) = \\frac{1}{1 - B(z)}``.
 """
 function MSET(z,max)
-    z = SymPy.symbols("z")
     n = SymPy.symbols("n")
     return(exp(summation(1/n * z^n,(n,1,max))))
 end