mvar -- main variable of a polynomial

• Usage:

  mvar f

• Inputs:
  • f, a ring element,
• Outputs:
  • a ring element, the main variable of f

i1 : R = QQ[x_0..x_3, MonomialOrder=>Lex];

i2 : f = x_1^2*(x_2*x_3+2*x_3) + x_1*(x_2^2-1) + (x_2-x_3)

      2         2        2
o2 = x x x  + 2x x  + x x  - x  + x  - x
      1 2 3     1 3    1 2    1    2    3

o2 : R

i3 : mvar f

o3 = x
      1

o3 : R