<Tr> <Td> ∣ ∤ </Td> <Td> ∣ (\ displaystyle \ mid \! \,) ∤ (\ displaystyle \ nmid \! \,) </Td> <Td> divisor, divides divides number theory </Td> <Td> a ∣ b means a divides b . a ∤ b means a does not divide b . (The symbol ∣ can be difficult to type, and its negation is rare, so a regular but slightly shorter vertical bar character is often used instead .) </Td> <Td> Since 15 = 3 × 5, it is true that 3 ∣ 15 and 5 ∣ 15 . </Td> </Tr> <Tr> <Td> ∣ ∣ </Td> <Td> ∣ ∣ (\ displaystyle \ mid \ mid \! \,) </Td> <Td> exact divisibility exactly divides number theory </Td> <Td> p ∣ ∣ n means p exactly divides n (i.e. p divides n but p does not). </Td> <Td> 2 ∣ ∣ 360 . </Td> </Tr> <Tr> <Td> ∥ ∦ ⋕ </Td> <Td> ∥ (\ displaystyle \ \! \,) </Td> <Td> parallel is parallel to geometry </Td> <Td> x ∥ y means x is parallel to y . x ∦ y means x is not parallel to y . x ⋕ y means x is equal and parallel to y . (The symbol ∥ can be difficult to type, and its negation is rare, so two regular but slightly longer vertical bar characters are often used instead .) </Td> <Td> If l ∥ m and m ⊥ n then l ⊥ n . </Td> </Tr> <Tr> <Td> incomparability is incomparable to order theory </Td> <Td> x ∥ y means x is incomparable to y . </Td> <Td> (1, 2) ∥ (2, 3) under set containment . </Td> </Tr>

What does the triangle mean in math equations