Operators + and -

+ (resp -) is an infixed function and '+' (resp '-') is a prefixed fonction. The result depends on the nature of its arguments.
Examples with + (all examples except the last one work also with - instead of +) :

• input (1,2)+(3,4) or (1,2,3)+4 or 1+2+3+4 or '+'(1,2,3,4), output 10,
• input 1+i+2+3*i or '+'(1,i,2,3*i), output 3+4*i,
• input [1,2,3]+[4,1] or [1,2,3]+[4,1,0] or '+'([1,2,3],[4,1]), output [5,3,3],
• input [1,2]+[3,4] or '+'([1,2],[3,4]), output [4,6],
• input [[1,2],[3,4]]+ [[1,2],[3,4]], output [[2,4],[6,8]],
• input [1,2,3]+4 or '+'([1,2,3],4), output poly1[1,2,7],
• input [1,2,3]+(4,1) or '+'([1,2,3],4,1), output poly1[1,2,8],
• input "Hel"+"lo" or '+'("Hel","lo"), output "Hello".