input: Write a python function to check if the triangle is valid.
  assert valid_triangle(3, 4, 5) == True
  assert valid_triangle(1, 10, 12) == False
  assert valid_triangle(7, 10, 5) == True
  assert valid_triangle(0, 4, 5) == False
output: def valid_triangle(a, b, c):
      return a + b > c and a + c > b and b + c > a and a > 0 and b > 0 and c > 0