Plus

(e1 + e2 + ...) computes the sum of all expressions in the function.

Attributes[Plus] := {Flat, Listable, NumericFunction, OneIdentity, Orderless, Protected}

Simple examples

In[1]:= 1 + 1
Out[1]= 2

If Reals are present, other Integers are demoted to Reals:

In[2]:= (5.2 + 0.2*-1) + 5*-1
Out[2]= 0.

Plus automatically combines like terms:

In[3]:= a + b^2 + 5*b^2
Out[3]= a + 6*b^2

In[4]:= (a + b) + (a + b)*-1 + c + c*-1 + 2*c^a + 2*d + 5*d + d + (5*d)*-1 + 3*c^a
Out[4]= 5*c^a + 3*d

In[5]:= 4*a*b*c*d*e*f - 7*a*b*c*d*e*f
Out[5]= -3*a*b*c*d*e*f