Tinjauan kebijakan hukum pertambangan yang berkeadilan bagi investor dan pemerintah pasca berlakunya UU No 4 2009 tentang pertambangan mineral dan batubara: studi kasus PT X sebuah perusahaan penanaman modal asing di bidang pertambangan nikel = Review of equitable law in mining policies for both investor and government after the enactment of law No 4 year 2009 concerning mineral and coal mining: case study of PT X a foreign investing company within business scope of nickel mining