@C01258@ referring to torsion angles θ (A, B, C, D), where A, B, C, D are main-chain atoms, can be described as: cis or @T06406-1@ (\(\text{C}\)); @G02593@ or @T06406-2@ (\(\text{G}\)); @T06406-4@ (\(\text{A}\)); and @C01092@ or @T06406-3@ (\(\text{T}\)), corresponding to torsion angles within ± 30° of, respectively, 0°, ± 120° and ± 180°. The letters shown in parentheses (upper case \(\text{C}\), \(\text{G}\), \(\text{A}\), \(\text{T}\)) are the recommended abbreviations. The symbols \(\text{G}^{+}\), \(\text{G}^{-}\) (or \(\text{A}^{+}\), \(\text{G}^{-}\), for example) refer to torsion angles of similar type but opposite known sign, i.e. ~ +60°, ~ -60° (or ~ +120°, -120°). The notation \(\text{G}\), \(\bar{\text{G}}\) ; \(\text{A}\), \(\bar{\text{A}}\) (and \(\text{T}\), \(\bar{\text{T}}\) ; \(\text{C}\), \(\bar{\text{C}}\) - whenever the torsion angles are not exactly equal to 180° and 0°, respectively) is reserved for the designation of @E02079@ conformations, i.e. conformations of opposite but unspecified sign. Where necessary, a @D01650@ from the proper value of the @T06406-5@ can be indicated by the sign (~), as in the following examples: \(\text{G(~)}\); \(\text{G}^{+}\text{(~)}\); \(\text{G}^{-}\text{(~)}\).