Puppies are small.
If it is a puppy, then it is small.
If x is odd, then 3x is odd.
If x is even, then 3x is even.
If the child is 5 years old, then he/she is in kindergarten.
If the child is in kindergarten, then he/she is 5 years old.
If air is gas, then water is liquid.
If water is not liquid, then air is not gas.
All carnivores are meat-eating animals.
If the animals are carnivores, then they are meat-eating animals.
If you are a junior high school student, then you are in primary level.
If you are not a junior high school student, then you are not in primary level.
If a polygon has five sides, then it is a pentagon.
If the polygon is a pentagon, then it has five sides.
If x is odd, then 2x is even.
If 2x is odd, then x is even.
A line contains at least 2 points.
If it is a line then it contains at least 2 points.
If two segments have the same length, then they are congruent.
If the two segments do not have the same length, then they are not congruent.
If two planes intersect, then their intersection is a line.
If their intersection is a line, then the two planes intersect.
If a point lies on two lines, then it is at the intersection.
If a point is not at the intersection, then it does not lie on two lines.
A plane contains at least 3 non-collinear points.
If it is a plane, then it contains at least 3 non-collinear points.
If the measure of angle p is 90 degrees, then it is a right angle.
If the measure of angle p is not 90 degrees, then it is not a right angle.
If x+3=10, then x=7.
If x+3≠ 10, then x≠ 7.
If the triangle is isosceles, then it has two equal sides.