Question about definition in armv8 memory model

Hi exports:

In ARMv8 spec(K_a), it says:

A Memory Read effect E2 Reads-from-memory a Memory Write effect E1, if and only if E1 and E2 are to the same location and E2 takes its data from E1.

A Memory Read effect E2 of a Location is the Local read successor of a Memory Write effect E1 to the same Location if E1 appears in program order before E2 and there is no Memory Write effect E3 to the same Location appearing in program order between E1 and E2.

what the difference  between them 

An example would be better, thanks very much.