2. prove or disprove following by giving examples: (15 points) (a) if x ⊂ y and x ⊂ z, then x ⊂ y ∩ z yes (b) if x ⊆ y and y ⊆ z, then x ⊆ z yes (c) if x ∈ y and y ∈ z, then x ∈ z