formal主要用于等价性检查，检查步骤如下：
1.Read design
2.Set up
3.Matching：Map corresponding signals between pairs of designs
4.Verification：Compare the logic cones that drive the mapped signals
二：逻辑锥的概念：
A logic cone consists of combinational logic originating from a specific design object and fanning backward to terminate at certain design object outputs.
三：Compare Points
A compare point is a design object used as a combinational logic endpoint during verification
Formality uses the following design objects to create compare points automatically:
• Primary outputs
• Sequential elements
• Black box input pins
• Nets driven by multiple drivers, where at least one driver is a port or black box
