Consider the points $P$ =$(0,0)$,$Q$ = $(1,0)$, $R$=  $(2,0)$, $S$ =$(3,0)$ in the $xy$-plane. Let $A,B,C,D$ be four finite sets of colours(not necessarily distinct nor disjoint). In how many ways can $P,Q,R$ be coloured bu colours in $A,B,C$ respectively if adjacent points have to get different colours? In how many ways can $P,Q,R,S$ be coloured by colours in $A,B,C,D$ respectively if adjacent points have to get different colors?
To solve this problem, we need to determine the number of ways to color the points \(P, Q, R\) and \(P, Q, R, S\) such that adjacent points have different colors. We will consider the sets \(A, B, C, D\) as sets of available colors for each point.

### Part 1: Coloring \(P, Q, R\)

1. **Coloring Point \(P\):**
   - Point \(P\) can be colored in any of the colors from set \(A\).
   - Let the number of colors in set \(A\) be \(|A|\).

2. **Coloring Point \(Q\):**
   - Point \(Q\) must be colored differently from \(P\).
   - Therefore, \(Q\) can be colored in any of the colors from set \(B\) except the color used for \(P\).
   - Let the number of colors in set \(B\) be \(|B|\).
   - The number of choices for \(Q\) is \(|B| - 1\).

3. **Coloring Point \(R\):**
   - Point \(R\) must be colored differently from \(Q\).
   - Therefore, \(R\) can be colored in any of the colors from set \(C\) except the color used for \(Q\).
   - Let the number of colors in set \(C\) be \(|C|\).
   - The number of choices for \(R\) is \(|C| - 1\).

Combining these choices, the total number of ways to color \(P, Q, R\) is:
\[
|A| \times (|B| - 1) \times (|C| - 1)
\]

### Part 2: Coloring \(P, Q, R, S\)

1. **Coloring Point \(P\):**
   - Point \(P\) can be colored in any of the colors from set \(A\).
   - Let the number of colors in set \(A\) be \(|A|\).

2. **Coloring Point \(Q\):**
   - Point \(Q\) must be colored differently from \(P\).
   - Therefore, \(Q\) can be colored in any of the colors from set \(B\) except the color used for \(P\).
   - Let the number of colors in set \(B\) be \(|B|\).
   - The number of choices for \(Q\) is \(|B| - 1\).

3. **Coloring Point \(R\):**
   - Point \(R\) must be colored differently from \(Q\).
   - Therefore, \(R\) can be colored in any of the colors from set \(C\) except the color used for \(Q\).
   - Let the number of colors in set \(C\) be \(|C|\).
   - The number of choices for \(R\) is \(|C| - 1\).

4. **Coloring Point \(S\):**
   - Point \(S\) must be colored differently from \(R\).
   - Therefore, \(S\) can be colored in any of the colors from set \(D\) except the color used for \(R\).
   - Let the number of colors in set \(D\) be \(|D|\).
   - The number of choices for \(S\) is \(|D| - 1\).

Combining these choices, the total number of ways to color \(P, Q, R, S\) is:
\[
|A| \times (|B| - 1) \times (|C| - 1) \times (|D| - 1)
\]

The final answer is \( \boxed{ |A| \times (|B| - 1) \times (|C| - 1) } \) for \(P, Q, R\) and \(|A| \times (|B| - 1) \times (|C| - 1) \times (|D| - 1)\) for \(P, Q, R, S\).