PROBLEM in function PART, part({x,y^2}) returns → "x"

[compsystems]

a: part(sin(x)) → 1 // OK 1 part or argument
a1: part(sin(x),1) → x // OK argument of SIN
a2: part(sin(x),0) → "sin" // OK operator "SIN"
a3: part(sin(x),2) → "Error: Bad Argument Value" // OK there is only one part according to previous result ITEM (a)


b: part(exp(y)) → 1 // OK 1 part or argument
b1: part(exp(y),1) → y // OK argument of EXP
b2: part(exp(y),0) → "exp" // OK operator "EXP"
b3: part(exp(y),2) → "Error: Bad Argument Value" // OK there is only one part according to previous result ITEM (b)

c: part(e) → 1 // OK 1 part or argument /! argument exp(1)==e
c1: part(e,1) → 1 //
c2: part(e,0) → "exp" // OK operator "EXP"
c3: part(e,2) → "Error: Bad Argument Value" // OK there is only one part according to previous result ITEM (c)

d: part(i) → 0 // OK 0 parts
d1: part(1,0) → "i" // OK as no operator input is returned as a string
d2: part(i,2) → "Error: Bad Argument Value" // OK there is not parts according to previous result ITEM (d)
d3: part(i,1) → i BUG contradiction with ITEM (d) within a program that causes a bad outing,

d2: part(i,-1) → i
may be valid assume -1 if no parts and if desired return same input,