## Simple input and output cells

x(n):=sum(x[i],i,1,n)$

x;

x+
y;

x(1)=1;x(10)=1;x(100)=1;

a*b;
aa*b;
a*bb;
a_1*b;
a_1*bb;
a*b_1;
aa*b_1;