Proposes a move in state space.
Combines propoosals by randomly selecting from two groups of operators
| type: beast.base.inference.Operator*** |
| operator for doing first proposal |
| Required input |
| type: beast.base.inference.Operator*** |
| operator for doing second proposal |
| Required input |
| type: java.lang.Double |
| weight with which this operator is selected |
| Required input |