Mermaid snippet:

		
flowchart TB
A --> C
A --> D
B --> C
B --> D
		
	

More complex case:

		
sequenceDiagram
participant Alice
participant Bob
Alice->>John: Hello John, how are you?
loop Healthcheck
	John->>John: Fight against hypochondria
end
Note right of John: Rational thoughts 
prevail!
John-->>Alice: Great!
John->>Bob: How about you?
Bob-->>John: Jolly good!