
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given a triangle $ABC$, where the sides opposite angles $A$, $B$, and $C$ are $a$, $b$, and $c$, respectively, and satisfying $\frac {\sin (A+B)}{\sin A+\sin B}= \frac {a-b}{a-c}$.
(Ⅰ) Find the value of $B$;
(Ⅱ) If $b= \sqrt {3}$, find the maximum value of the area of $\triangle ABC$, $S$.

Present the answer in LaTex format: \boxed{Your answer}
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