Art De La Guerre

[Kal5056]

You cannot attack a flank unless you start on a flank
You cannot charge a unit if you start in contact even by a corner to corner

You can conform (just fight regular no impact). This is free as you are not in position to support a combat 
Or
Move away
Or
Stay there 

If you stay there then the opponent has same options. 

Gino

[Black Prince]

If YYYY is impetuous then it is compulsory for YYYY to conform unless you hold YYYY with 3 pips

[lionelrus]

[fritz]

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[Ramses II]

If YYYY is Impetuous then

• If it defeated it’s opponenent in its turn it must pursue (p62) 
  
• If it defeated its opponent in the opposing players turn, it must conform at the start of its own turn (p55)

[Mike Bennett]

I thought p55, even for impetuous it was only compulsory if "subject to an uncontrolled charge". So you can

spend pips and move, so no uncontrolled charge
Spend no pips and conform as an uncontrolled charge

[Ramses II]

True, my bad