However , the idea that a closed metabolic cycle , such as the reductive citric acid cycle , could form spontaneously ( proposed by GÃ 1\/4 nter WÃ chtershÃ user ) remains unsupported . However , the idea that a closed metabolic cycle , such as the reductive citric acid cycle , could form spontaneously ( proposed by GÃ 1\/4 nter WÃ chtershÃ user ) remains debated .