
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 that $\overrightarrow {i}$ and $\overrightarrow {j}$ are mutually perpendicular unit vectors, $\overrightarrow {a}= \overrightarrow {i}-2 \overrightarrow {j}$, $\overrightarrow {b}= \overrightarrow {i}+\lambda \overrightarrow {j}$ and the angle between $\overrightarrow {a}$ and $\overrightarrow {b}$ is acute, determine the range of the real number $\lambda$.

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