Conformations referring to torsion angles θ (A, B, C, D), where A, B, C, D are main-chain atoms, can be described as: cis or synperiplanar ($\text{C}$); gauche or synclinal ($\text{G}$); anticlinal ($\text{A}$); and trans or antiperiplanar ($\text{T}$), 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 $\text{G}$, $\overline{\text{G}}$ ; $\text{A}$, $\overline{\text{A}}$ (and $\text{T}$, $\overline{\text{T}}$ ; $\text{C}$, $\overline{\text{C}}$ - whenever the torsion angles are not exactly equal to 180° and 0°, respectively) is reserved for the designation of enantiomorph conformations, i.e. conformations of opposite but unspecified sign. Where necessary, a deviation from the proper value of the torsion angle can be indicated by the sign (~), as in the following examples: $\text{G(~)}$; ${\text{G}}^{+}\text{(~)}$; ${\text{G}}^{-}\text{(~)}$.